There are several reasons for monitoring the core temperature of ruminant animals, including determination of sickness or disease and for breeding purposes. Temperature changes of one degree Fahrenheit or less can signal a change in the physiological state of a ruminant animal. Early detection of such physiological changes would allow ranchers, feed lot operators, dairymen and others to take necessary action to prevent the spread of sickness and disease, to treat a sick or diseased animal in a timely manner, or to monitor breeding conditions.
The problem of monitoring the temperature of individual animals in a herd becomes complicated, especially when the herd is allowed to roam over a wide area. In order to monitor the temperature of individual animals in a herd, it is necessary to correlate temperature measurements with specific animals.
Several attempts have been made to provide systems for remotely monitoring the temperature of animals.
U.S. Pat. No. 5,482,008 to Stafford et al. discloses an electronic animal identification system which includes a bolus that is administrated into the rumen or reticulum of a ruminant animal. The bolus includes an electronic identification device and an optional temperature sensor. In operation, boluses transmit the identification and temperature data only in response to an interrogation unit outside the animal.
U.S. Pat. No. 4,399,821 to Bowers discloses a free moving animal physiological monitoring and identification system which includes an implanted device which may be swallowed and located in the stomach of an animal. The system utilizes a parameter interrogator to obtain temperature data from the implant.
U.S. Pat. No. 4,262,632 to Hanton et al. discloses an electric livestock identification system which includes a transmitter capsule which can be placed in the reticulum of an animal. An interrogator-receiver unit is used to power the capsule and receive identification data.
U.S. Pat. No. 3,893,111 to Cotter discloses a system for remote monitoring of animal temperature which includes a capsule that contains a variable length antenna which changes in length according to temperature. The capsule is embedded into an animal and activated by a remote interrogation unit.
Collectively, prior art devices which are designed to remotely monitor animals such as cows suffer from a number of similar problems which render the systems in which they are used less than satisfactory both from manufacturing and performance stand points.
For example, the data transmission ranges for known prior art devices are limited to six meters or less. This limitation renders such devices and their related systems unacceptable for monitoring animals which are allowed to roam freely. Although one solution for this problem is the use of a network of receivers with overlapping ranges, the cost for such a system can be prohibitive. Moreover, there are failure and maintenance problems which increase with increasing numbers of receivers, as well as potential power supply problems.
Identification codes which are presently used in animal monitoring devices are set during manufacturing, so that a user of such devices is required to order a series of sequentially coded devices. Care has to be taken to keep track of the identification code of each device. Moreover, when herds of animals are mixed together or within the proximity of a common receiver, it is possible for two or more devices to transmit similar identification codes.
Battery life of implanted monitors is severely limited in prior art systems. Although the solution for extending battery life has been to limit data transmission to times when the monitors are interrogated, the actual battery life of such monitors is far less than the expected life or service life of the animals. Accordingly, once the batteries in an implanted device fail, an additional implanted device must be incorporated into the animal. Adding additional objects into the rumen or reticulum of a ruminant animal may not be desirable.
Another disadvantage with interrogating the implanted devices is that the need for interrogation limits the range at which the devices can be used. Although this is not a problem since the actual useful ranges of known devices are inherently limited, the requirement of interrogation does enforce the useful range limitations on systems using the prior art monitors.
Prior art devices which include temperature sensors, involve a trade-off between temperature accuracy and the cost of circuit tuning elements, thereby requiring that each implanted device be individually tuned and calibrated. Such individual tuning and calibration adds addition expense to manufacturing costs which are compounded by the circuit tuning elements. Prior art devices such as U.S. Pat. No. 3,893,111 to Cotter which use mercury containing temperature sensors can be hazardous if they malfunction and leak mercury.
Prior art systems in general are susceptible to magnetic and electrical interference to the point that they will display incorrect data or become desensitized and fail to operate at all.
Magnetic interference can result from implants being too close in proximity to magnets. In this regard, it is common practice to insert magnets which permanently reside in the reticulum of animals to attract and collect magnetic objects so that such objects do not pass through the gastrointestinal tract of the animal and cause health problems. Implanted monitors or sensors can become lodged in close proximity to such magnets and thus be adversely affected by their magnetic fields.
The circuitry in prior art implanted devices may also be subject to electrical interference which effects detuning of the resonant frequency of the devices' antennas. Such electrical interference can result if the devices are in close proximity to magnets or any other conductive materials.
The present invention provides an ingestible temperature sensor that has a number of advantages over prior art devices.